Acoustic impedance transformer



1960 c. KLEESATTEL 2,948,154

ACOUSTIC IMPEDANCE TRANSFORMER Filed Feb. 16, 1956 11 6 I l M /0 I 22 20,SH ess INVENTOR C'Lm/s KLEESATTZL fi l/w L E ATTORN EYS ACOUSTIC EDANCETRANSFORMER Claus Kleesattel, Kew Gardens, N.Y., assignor to CavitronCorporation, a corporation of New York Filed Feb. 16, 1956, Ser. No.565,905

8 Claims. (Cl. 74-1) The present invention relates to acoustic impedancetransformers of the type utilized for transmitting ultrasonicvibrationsto a tool from an electromechanical "transducer such as amagnetostrictive transducer. Acoustic impedance transformers are used,for example, in ultrasonic cutting or drilling processes of the typedisclosed and claimed in Balamuth Patent No. 2,580,716 dated January 1,1952. g

The new transformer, or tool holder, of the present invention isparticularly suitable for use in ultrasonic drilling equipment such asis now employed in dental applications wherein the hand piece comprisesa maghetostrictive transducer, an acoustic impedance transformer or toolholder secured at one end to an end of the transducer and a tool securedto the other end of the tool holder. The transformer or tool holderserves "to transmit to the tool longitudinal vibrations generated in thetransducer and to increase the amplitude of such vibrations. Variousshapes of transformers or tool holders have been used, includingexponentially tapered tool holders, conical tool holders, multiplesection cylindrical tool holders and the like. The tool holder should beof such length that during operation at the operating frequency a loopof motion of the longitudinal vibrations occurs at or near the toolattaching end of the holder. The total stress comprising the sum of theaxial stress and the radial stress developed varies along the holderwith the distance from a node and with the configuration of the holder.Any abrupt change in cross sectional area causes an abrupt stress rise.A tool holder employed in ultrasonic equipment is ordinarily providedat.its end with a short axial threaded aperture for reception of thethreaded stud of a tool. The stress rise occasioned by the abrupt changein cross sectional area at the base of the aperture weakens the toolholder at such location, creating a tendency to crack or break in theregion of the aperture. An object of the present invention is thereforeto minimize abrupt variation in total stress along the length of thetransformer and particularly at the'tool end thereof to thereby reducedanger of breakage.

V In the practice of ultrasonic drilling. processes it is necessary tochange the tool at relatively frequent in tervals. For this reason thetool is attached to the tool holder by screw threads. Frequent change oftool tends towear the threads and shorten the life of the holder.Furthermore, when the tool is short, the abrasive slurry employed in thedrilling process of the said Balamuth patent tends to penetrate thescrew threads. This results in greater wear of the threads and furthershortens the useful life of the tool holder. Another. objectof the"invention, therefore, is to provide means for protecting theithrea dedend of the tool holder and thereby to increase the useful life of theequipment.

, 2,948,154 Patented Aug. 3,1960

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the location of a node of motion of the longitudinal vibrationstransmitted by the holder and by providing a conformation of tool holderwhich substantially eliminates abrupt changes in cross sectional area.The longitudinal passage at the tool end of. the transformer isthreaded. This construction results in a tool holder having no abruptstress rise along the length but with a relatively extended high stresszone intermediate its ends. The extension of the threaded. aperture intoa relati vely long passage which extends to or beyond the node avoidsthe abrupt stress rise heretofore resulting at the point of connectionto the tool. In the preferred embodiment of the invention wear of thethreads of the tool holder is avoidedby the provision of an intermediatecoupling memberbetween the tooland transformer whichv threads into thepassage in the tool holder and into which the tool is threaded. Thecoupling member is preferably made of a metal of great strength andlowdensity, such as titanium, and the two threaded sections thereof, theone section for connection to the tool holder and the other forreception of the threads of the tool, are of different pitch-diameterratio to avoid loosening of the coupling member in the tool holderduring removal of a tool. The coupling member may thus be removed andreplaced when the threaded connection between the tool and the couplingmember becomes fouled as a result of an improved acoustic impedancetransformer and coupling member embodying the invention;

Fig. 2 is a graph showing the variation in stress, both axial andradial, along the transformer of Fig 1; and Fig. 3 is a graph showing.the change in amplitude along the transformer of the compressional wavestransmitted thereby during operation of the equipment 7 y In Fig. 1 atool holder or acoustic impedance transformer 2 embodying the inventionis shown. as fixedly connected at one end to an end of amagnetostrictive transducer 4. and is coupled at its other end throughthe intermediary of a coupling element 6 to a tool 8 Themagnetostrictive transducer 4, which may beof any well knownconstruction, has been schernatically and but partially illustrated inthe drawing, as including a laminated stack 10 of nickel or other;magnetostrictive material provided with a slot 12 through which isthreaded the turns of an energizing winding-14. It will be understoodthat high frequency alternating current together with a suitable directcurrent for proper bias will be delivered to the coil l ifrom anysuitable source (not shown). compressional waves generated in the stack10 are transmitted through the transformer 2 and coupling 6- to thetool-8.. The transformer or tool holder 2 and magnetostrictivetransducer4 are fixedly secured together, as by soldering, and. thedimensions of the transducer are such that during. energization at theoperating frequency say, 25 he, a loop ofmotion occurs at the junctionbetween the tool holder and transducer. In the particular embodimentofthe invention illustrated in Fig. l the transformer 2 comprises acylindrica'l one-quarter wavelength input sectionterminating intheregion of a node of motion indicated by the broken line' 16 andv aone-quarter wavelength output section the cross sectional area of whichgradually'decreases from the inputend to a minimum cross: section in theneighborhood of the broken lineldand. then increases gradually-to mergewith a cylindrical end portio'n 20 of a diameter substantially lesstha'nthatof the cylindrical input section of the transformer. The transformeris provided with a longitudinal axial passage 22 which extends for theentire length of the two sections and is threaded in the region of theopen end thereof ,within the cylindrical portion'20. f The tool 8 could.be directly secured to the output section of the transformer by means ofthe threads within the passage 22 and for some purposes such anarrangement would be satisfactory, for example, where tool change wasonly desired after relatively long use of a tool and where the tool wasintended for operation without the use of an abrasive slurry.Preferably, to reduce wear on the threads of the transformer and therebyto prolong the useful life thereof, there is provided a coupling member6 having a threaded stud 24 thereon, the threads of which mate with thethreads of the transformer. The coupling 6 is provided with an axialthreaded passage 26 for reception of the threaded stud of the tool. Thecoupling member 6 should be of light strong material. Titanium has beenfound in practice to be particularly suitable for this purpose, butother materials, such as steel or Monel could be used. Threads of adifferent pitch-diameter ratio are used in the coupling member 6 toavoid any tendency of loosening of member 6 in the transformer duringremoval of a tool.

Because there is no abrupt change in cross sectional area of thetransformer 2, when constructed of the configuration above describedwith reference to Fig. 1, there is no abrupt change in total stressalong the length of the transformer which could lead to dangerous stresspeaks and fracture of the tool holder.

In the graph of Fig. 2, where the ordinates represent stress on anarbitrary scale and the abscissae represent distance along the toolholder 2 and coupling member 6, the curve A illustrates typicalvariation of the longitudinal stress in a holder of the configuration ofFig. 1 when transmitting vibrations at the operating frequency. Curve Brepresents the combined longitudinal and radial stress. It will beapparent that although curve B indicates a relatively extended zone ofhigh stress, that between the lines indicated by the reference numerals28 and 30, there is no abrupt stress rise over the length of the holder.Moreover the total stress at the neighborhood of the threaded connectionbetween the coupling member 6 and the tool holder 2 is relatively low,actually slightly less than that at the node. The shape of the stresscurve B indicates that the transformer or holder of Fig. 1 will not haveany critically weak zone where breakage is apt to occur, and therefofrecan be expected to have a relatively long operating In Fig. 3, variationin amplitude of the compressional wave transmitted by the transformer 2when the transducer is energized at the operating frequency isillustrated by the curve C. The magnification efiected by the shape ofthe transformer 2 of Fig. l is apparent from a comparison of theamplitude a at the input end with the larger amplitude at at the outputend of the transformer. It will be noted that the gradual and slightincrease in cross sectional area of the output section of thetransformer, beginning at line 18 and merging into the short cylindricalsection 20 has but a relatively small effect in reducing the amplitudeof vibrations at the output end of the transformer and coupling, whilethe overall eifect of the transformer is to magnify the amplitude ofvibration of the compressional waves.

The increase in cross sectional area at the output end serves to giveadditional strength along the threaded region. The provision of theremovable and replaceable coupling member adds substantially to .thelife of the entire equipment.

The invention has now been described with reference to a singleembodiment thereof. Various changes, with in the scope of theaccompanying claims, could be made in the particular configuration ofthe acoustic impedance transformer. For example, a shorter longitudinalpassage could be employed, one jterminating in the neighborhood of anode of motion of the longitudinal vibrations, or the minimum crosssectional area of the holder could be at the tool end thereof, ratherthan short of the end as in the illustrated embodiment. Other variationswill occur to those skilled in the art.

Although a magnetostrictive transducer has been shown and described asthe source of the longitudinal vibrations transmitted by the newacoustic impedance transformer, obviously the invention is not limitedto such specific type of transducer.

The following is claimed:

1. An acoustic impedance transformer for transmission of longitudinalvibrations from an electromechanical transducer to a tool, comprising aninput section fixed at one end to the transducer, an output sectionintegral at one end with the other end of said input section, saidoutput section having a longitudinal open ended axial passage thereinextending therethrough, the cross sectional area of said output sectionbeing greater at the input end than at the output end, and being aminimum intermediate the input and output ends, the change in crosssectional area along the length of the output section being gradual toprevent abrupt change in total stress, the wall of said passage adjacentthe output end thereof being provided with screw threads, and a couplingmember of hard, light weight material and provided with a stud havingscrew threads therein adapted to mate with the threads on the Wall ofsaid passage, said coupling member being provided with means for readyattachment thereto of a tool.

2. An acoustic impedance transformer for transmission of longitudinalvibrations from an electromechanical transducer to a tool, comprising aninput section fixed atone end to the transducer and an output sectionintegral at one end with the other end of said input section, saidoutput section having a longitudinal open ended axial passage thereinextending therethrough, screw threads formed on the interior wall ofsaid axial passage at the output end of said output section, the crosssectional area of said output section gradually diminish- .ing from amaximum at the input end to a minimum short of the output end andgradually increasing from the minimum to a magnitude at the output endsubstantially less than at the input end, whereby during transmission oflongitudinal vibrations of a frequency such that a node of motion occursat the junction of the input and output sections there is an extendedhigh stress zone in the region of the minimum cross sectional area ofthe output section but no abrupt stress rise at any point along theoutput section; and a coupling member of hard, light weight material andprovided with a stud having screw threads therein adapted to mate withthe threads on the interior wall of said axial passage, said couplingmember being provided with means for ready attachment of a tool thereto.

, 3. An acoustic impedance transformer for transmitting longitudinal\u'brations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a total wave length approximately corresponding to onehalf thewave length or multiples thereof at the vibration frequency injectedinto the input end thereof by the transducer as fixed thereto, saidtransformer presenting an input section of substantial uniform crosssectional area and a variable cross sectional area output sectionintegral with the input section, said output section having a wavelength substantially equal to the wave length of the input section tothereby provide a node of motion at the area of juncture, said outputsection having a tool attaching end portion of substantially uniformcross sectional area, said output section having a gradually decreasingcross sectional area extending from its nodal juncture with said inputsectionto the intermediate region thereof and thence having a graduallyincreasing cross sectional area extending from said intermediate regionto its juncture with said end portion, said end portion having a crosssectional area greater than the cross sectional area of the intermediateregion of said output section but of lesser cross sectional area thanthe nodal juncture of said output section with said input section,whereby an extended high stress zone is provided in the intermediateregion of the output section but no abrupt stress zone occurs at anypoint along the length of the transformer.

4. An acoustic impedance transformer for transmitting longitudinalvibrations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a longitudinal passage extending axially therethrough and totalwave length approximately corresponding to one-half the wave length ormultiples thereof at the vibration frequency injected into the input endthereof by the transducer as fixed thereto, said transformer presentingan input section of substantial uniform cross sectional area and avariable cross-sectional area output section integral with the inputsection, said output section having a Wave length substantially equal tothe wave length of the input section to thereby provide a node of motionat the area of juncture, said output section having a tool attaching endportion of substantially uniform cross sectional area,

said output section having a gradually decreasing cross sectional areaextending from its nodal juncture with said input section to theintermediate region thereof and thence having a gradually increasingcross sectional area extending from said intermediate region to itsjuncture with said end portion, said end portion having a crosssectional area greater than the cross sectional area of the intermediateregion of said output section but of lesser cross sectional area thanthe nodal juncture of said output section With said input section,whereby an extended high stress zone is provided in the intermediateregion of the output section but no abrupt stress zone occurs at anypoint along the length of the transformer.

5. An acoustic impedance transformer for transmitting longitudinalvibrations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a total wave length approximately corresponding to onehalf thewave length or multiples thereof at the vibration frequency injectedinto the input end thereof by the transducer as fixed thereto, saidtransformer presenting a cylindrical input section of substantiallyuniform cross sectional area and a variable cross sectional area outputsection integral with the input section, said output section having awave length substantially equal to the Wave length of the input sectionto thereby provide a node of motion at the area of juncture, said outputsection having a cylindrical tool attaching end portion of substantiallyuniform cross sectional area, said output section having a graduallydecreasing cross sectional area extending from its nodal juncture withsaid input section to the intermediate region thereof and thence havinga gradually increasing cross sectional area extending from saidintermediate region to its juncture with said end portion, said endportion having a cross sectional area greater than the cross sectionalarea of the intermediate region of said output section but of lessercross sectional area than the nodal juncture of said output section withsaid input section, whereby an extended high stress zone is provided inthe intermediate region of the output section but no abrupt stress zoneoccurs at any point along the length of the transformer.

6. An acoustic impedance transformer for transmitting longitudinalvibrations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a longitudinal passage extending axially therethrough and '6total Wave length-approximately corresponding to one half the wavelength or multiples thereof at the vibration frequency injected into theinput end thereof by the transducer as fixed thereto, said transformerpresenting' a cylindrical input section of substantial cross sectionalarea and a variable crosssectional-area output section integral with theinput section, said output section having a wave length substantiallyequal to the Wave length of the input section to thereby provide a nodeof motion at the area of juncture, said ou't'put section having acylindrical tool attaching end portion of substantially uniform crosssectional area, said output section having a gradually decreasing crosssectional area extending from its nodal juncture with-said input sectionto the intermediate region thereof and thence having a graduallyincreasing cross sectional area extending from said intermediate regionto its juncture with said end portion, said end portion having a crosssectional area greater than the cross sectional area of the intermediateregion of said output section but oflesser cross sectional area than thenodal juncture of said output section with said input section, wherebyan extended high stress zone is provided in the intermediate region ofthe output section but no abrupt stress zone occurs at any point alongthe length of the transformer.

7. An acoustic impedance transformer for transmitting longitudinalvibrations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a total wave length approximately corresponding to onehalf thewave length or multiples thereof at the vibration frequency injectedinto the input end thereof by the transducer as fixed thereto, saidtransformer presenting an input section of substantial uniform crosssectional area and a variable cross sectional area output sectionintegral with the input section, said output section having a wavelength substantially equal to the wave length of the input section tothereby provide a node of motion at the area of juncture, said outputsection having a tool attaching end portion of substantiallyuniformcross sectional area and presenting a threaded bore, said output sectionhaving "a gradually decreasing cross sectional area extending from itsnodal juncture with said input section to the intermediate regionthereof and thence having a gradually increasing cross sectional areaextending from said intermediate region to its juncture with said endportion, said end portion having a cross sectional area greater than thecross sectional area of the intermediate region of said output sectionbut of lesser cross sectional area than the nodal juncture of saidoutput section with said intput section whereby an extended high stresszone is provided in the intermediate region of the output section but noabrupt stress zone occurs at any point along the length of thetransformer; and a tool attaching coupling member presenting a bodysection snugly abutting against the terminal end of said transformer endportion and a threaded stud portion extending into a threaded boreformed in said end portion.

8. An acoustic impedance transformer for transmitting longitudinalvibrations of high frequency and small amplitude when rigidly attachedto the output end of an electromechanical transducer, said transformerhaving a longitudinal passage extending axially therethrough and totalwave length approximately corresponding to one-, half the wave length ormultiples thereof at the vibration frequency injected into the input endthereof by the transducer as fixed thereto, said transformer presentingan input section'of substantial uniform cross sectional area and avariable cross sectional area output section integral with the inputsection, said output section having a wave length substantialy equal tothe wave length of the input section to thereby provide a node of motionat the area of juncture, said output section having a tool attaching endportion of substantially uniform cross sectional area which presents athreaded bore,

said output section having a gradually decreasing cross sectional areaextending from its nodal juncture with said input section to theintermediate region thereof and thence having a gradually increasingcross sectional area extending from said intermediate region to itsjuncture with said end portion, said end portion having a crosssectional area greater than the cross sectional area of the intermediateregion of said output section but of lesser cross sectional area thanthe nodal juncture of said output section with" said input sectionwhereby an extended high stress zone is provided in the intermediateregion of the output section but no abrupt stress zone occurs at anypoint along the length of the transformer;

and a tool attaching coupling member presenting a body section tightlyabutting against the terminal end'of the 15 end portion of saidtransformer output section and a threaded stud portion extending intothe threaded bore of 1 said end portion.

References Cited in-the'file of this patent UNITED STATES PATENTS704,385 7 Schmidt July 8, 1902 2,580,716 Balamuth Jan. 1, 1952 2,651,148'Carwile' Sept. 8, 1953 2,680,333 Calosi June 8, 1954 2,704,333 Calosiet al, Mar. 15, 1955 2,723,386 Camp Nov. 8, 1955 Thatcher et al Dec. 18,1956

